Project Summary The development of genetically engineered mouse models (GEMMs) together with the advent of Cre- LoxP technologies and tissue-specific promoters has become excellent tools to assess the functional roles of cancer-associated genes. In recent years, several promoters have been successfully adapted to drive Cre expression specifically within the intestinal epithelium. These promoters have proven useful for manipulating gene expression in normal cells throughout intestinal tract; however, a genetic system that will specifically target intestinal tumors for transgene expression has not yet been developed. Therefore, this exploratory proposal aims to establish a novel mouse model in which the forced expression of a given transgene can be re-introduced through tamoxifen-controlled Cre expression in intestinal tumors. To achieve tumor-specific expression, we will use stearoyl-CoA desaturase (Scd)-3 gene locus as a promoter. We have recently found that Scd3 was consistently up-regulated in intestinal tumors, but not in normal mucosa, suggesting that it may serve as a specific intestinal tumor marker in mice. In Aim 1, we propose to generate Scd3-CreER+/- mice, and Cre activity is validated using a reporter mice. Optimal timing and duration of Cre activity and the efficiency of Cre-Lox recombination will be determined to establish a viable mouse model. In Aim 2, we will then characterize the efficiency of Scd3-CreER system in Apc?14/+ tumor model. Finally, in Aim 3, we will extend our analysis to chemically-induced colon cancer model to test the applicability of our Scd3-CreER+/- mice to additional cancer etiologies. We believe that the successful generation of this experimental mouse system will provide a way to test the impact of reactivation of suppressed tumor-associated genes directly within neoplastic tissue, and also enable us to examine the therapeutic effects associated with the functional restoration of the lost genes.